Effects of photodynamic therapy using Red LED-light combined with hypocrellin B on apoptotic signaling in cutaneous squamous cell carcinoma A431 cells.

Background: The incidence of cutaneous squamous cell carcinoma (cSCC) has been demonstrating yearly increases. cSCC is a malignant cancer and exerts a major impact on patients' health and quality of life. Thus, the development and use of novel therapies in the treatment of cSCC are needed. It has been reported that LED photodynamic therapy (LED PDT) mediated by Hypocrellin B and its derivatives, a second-generation photosensitizer, can induce apoptosis in a variety of tumor cells, However, its potential pro-apoptotic effects on cSCC have yet to be investigated.

Objective: This study aims to investigate the pro-apoptotic effects and molecular mechanisms of HB-LED PDT in cutaneous squamous cell carcinoma A431 cells (Subsequent abbreviation A431 cells). Such information can provide an important theoretical foundation for the clinical translation of HB-LED PDT in the treatment of cSCC.

Methods: 1. Effects of HB on A431 cells were determined using a Cell Counting Kit-8 assay, which method can indirectly reflect the number of living cells. In this way, this assay can then provide a means to identify the optimal concentrations of HB required for the induction of apoptosis in A431 cells. 2. The effects of HB-LED PDT on the morphology of A431 cells and changes in the nuclei after Hoechst33342 staining as determined using inverted fluorescent microscopy. 3. Use of the Annexin V-FITC test kit to detect levels of apoptosis in A431 cells in response to treatment with HB. Changes in reactive oxygen species and mitochondrial membrane potential following HB-LED PDT treatment in A431 cells were determined using fluorescence activated cell sorting (FACS). 4. Real-time quantitative PCR and Western Blot were applied to assess changes in several key factors involved in apoptosis including Bax, Bcl-2, and Caspase-3, at both transcription and translation levels. With these assays, it was possible to investigate the apoptotic signaling pathway in A431 cells in response to HB-LED PDT.

Results: HB-LED PDT inhibited proliferation activity and promoted nuclear fragmentation within these A431 cells. HB-LED PDT inhibited mitochondrial activity, increased reactive oxygen species production, and promoted apoptosis of A431 cells. In addition, several key factors in the apoptotic signaling pathway were increased at both the transcriptional and translational levels in A431 cells in response to the HB-LED PDT, indicating that the apoptotic signaling pathway was activated by HB-LED PDT.

Conclusion: HB-LED PDT induces apoptosis in A431 cells through a mitochondria-mediated apoptotic pathway. Such findings serve as an important foundation for the development of new approaches in the treatment of cSCC.